How Bears Power-Nap

For most people, staying in shape means getting regular exercise. Take a vacation from the gym and your hard-earned six-pack goes soft. But imagine if you could sleep for five months and still wake up fit as a fiddle. According to research described yesterday in the journal Nature, this, in fact, is just how bears emerge from hibernation.

Henry J. Harlow of the University of Wyoming and his colleagues found that hibernating black bears lose less than 23 percent of their strength during their 130-day winter slumber. Humans, in contrast, would experience a 90 percent strength loss if they were immobile for so long. Incredibly, when the team took muscle biopsies from denned bears in early and late winter, they found that the skeletal muscle cells did not dwindle in size or number¿nor did they lose their protein content or oxidative capacity.

The researchers suggest that the bears may be maintaining their muscles by drawing on protein reserves from elsewhere in the body, and by shivering. "Understanding these processes in hibernating bears," the team writes, "may provide new insight into treating muscle disorders and into the effects of prolonged hospital bed confinement, antigravity and long-distance space travel on humans."